/**
 * *****************************************************************************
 * Copyright 2011 See AUTHORS file.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 * ****************************************************************************
 */
package sg.atom.utils.repository.pool;

import sg.atom.utils.datastructure.collection.Array;

/**
 * A pool of objects that can be reused to avoid allocation.
 *
 * @author Nathan Sweet
 */
abstract public class Pool<T> {

    /**
     * The maximum number of objects that will be pooled.
     */
    public final int max;
    /**
     * The highest number of free objects. Can be reset any time.
     */
    public int peak;
    private final Array<T> freeObjects;

    /**
     * Creates a pool with an initial capacity of 16 and no maximum.
     */
    public Pool() {
        this(16, Integer.MAX_VALUE);
    }

    /**
     * Creates a pool with the specified initial capacity and no maximum.
     */
    public Pool(int initialCapacity) {
        this(initialCapacity, Integer.MAX_VALUE);
    }

    /**
     * @param max The maximum number of free objects to store in this pool.
     */
    public Pool(int initialCapacity, int max) {
        freeObjects = new Array(false, initialCapacity);
        this.max = max;
    }

    abstract protected T newObject();

    /**
     * Returns an object from this pool. The object may be new (from
     * {@link #newObject()}) or reused (previously {@link #free(Object) freed}).
     */
    public T obtain() {
        return freeObjects.size == 0 ? newObject() : freeObjects.pop();
    }

    /**
     * Puts the specified object in the pool, making it eligible to be returned
     * by {@link #obtain()}. If the pool already contains {@link #max} free
     * objects, the specified object is reset but not added to the pool.
     */
    public void free(T object) {
        if (object == null) {
            throw new IllegalArgumentException("object cannot be null.");
        }
        if (freeObjects.size < max) {
            freeObjects.add(object);
            peak = Math.max(peak, freeObjects.size);
        }
        if (object instanceof Poolable) {
            ((Poolable) object).reset();
        }
    }

    /**
     * Puts the specified objects in the pool. Null objects within the array are
     * silently ignored.
     *
     * @see #free(Object)
     */
    public void freeAll(Array<T> objects) {
        if (objects == null) {
            throw new IllegalArgumentException("object cannot be null.");
        }
        for (int i = 0; i < objects.size; i++) {
            T object = objects.get(i);
            if (object == null) {
                continue;
            }
            if (freeObjects.size < max) {
                freeObjects.add(object);
            }
            if (object instanceof Poolable) {
                ((Poolable) object).reset();
            }
        }
        peak = Math.max(peak, freeObjects.size);
    }

    /**
     * Removes all free objects from this pool.
     */
    public void clear() {
        freeObjects.clear();
    }

    /**
     * The number of objects available to be obtained.
     */
    public int getFree() {
        return freeObjects.size;
    }

    /**
     * Objects implementing this interface will have {@link #reset()} called
     * when passed to {@link #free(Object)}.
     */
    static public interface Poolable {

        /**
         * Resets the object for reuse. Object references should be nulled and
         * fields may be set to default values.
         */
        public void reset();
    }
}
